The present invention relates to a tire with a carbon black-containing, black-colored, circumferential tread of a cap/base construction, wherein said tread cap has a lug and groove configuration and wherein the outer surface of a major portion of said grooves are designed to be ground contacting, and a co-extruded thin outer non-carbon black-containing rubber layer of a non-black color wherein said outer rubber layer is integral with and circumferentially extends from the axial outer edge of said tread cap to include at least of a visible surface of at least one groove in said tread cap. In one aspect, said tread contains a pair of black colored, carbon black reinforced, tread miniwings which extend from the axial outer edge of the tread over a portion of the tire sidewall, wherein said thin outer rubber layer joins said miniwing and wherein said tread cap, tread base, tread miniwings and thin outer layer are co-extruded, co-cured and therefore integral with each other.
Tire treads are conventionally of rubber compositions which contain at least some carbon black reinforcement and are thereby black in color. For various reasons, it may desired to provide a tire with a tread of which at least a portion of the tread has a color which contrasts with the primary black color of the tire and therefore does not contain carbon black reinforcement.
Historically, a tire with a silica reinforced tread which contains only a minimal amount of carbon black reinforcement, if any, and which contains a co-extruded carbon black-containing thin outer rubber layer on its outer tread surface to serve as an electrically conductive path for static electricity for such tread has been proposed according to U.S. Pat. No. 6,044,882. Realistically, such tread may be black in color if it does contain only a minimal amount of carbon black or it may be of a non-black color if it does not contain carbon black. Therefore, conceivably such tread may be of a non-black color whereas the aforesaid thin outer rubber layer is of a black color and may extend from a tread miniwing. In such manner, then, a tire might be provided with a tread of which a part of its visible portion is of a color other than black.
Also historically, a typical example of a component of a tire having a color which contrasts with the conventional black color of the tire is a tire sidewall in which a portion of the rubber is white in color resulting from a blend of rubber and titanium dioxide pigment in the absence of, or exclusive of, particulate carbon black reinforcement. Tires with white colored portions of their sidewalls are well known.
However, it is appreciated that coloring pigments such as titanium dioxide do not provide significant rubber reinforcement equivalent to rubber reinforcing carbon black. Therefore, such tire components are conventionally limited to rubber compositions which do not need such a high degree of reinforcement.
It is also appreciated that such colored rubber compositions which contains a coloring pigment such as titanium dioxide have a tendency to discolor as a result of various discoloring chemicals which may be contained in various rubber compositions which are adjacent to the colored rubber composition. Accordingly, it is a common practice to use substitute non-discoloring chemicals for discoloring chemicals in such adjacent rubber compositions such as for example, non-discoloring antidegradants and non-discoloring rubber processing oils. Such practice is well known in the tire white sidewall art.
For this invention, it is desired to provide a tire having a tread having a portion which is of a visible color which contrasts with black-colored carbon black reinforced rubber and which does not require a majority of the outer surface of the tire which is intended to be ground-contacting to be of such contrasting color, and to thereby avoid especially compounding such contrastingly colored tread segments the surface of the tire intended to be ground-contacting have a wear and traction substantially equivalent to the black-colored carbon black reinforced tread rubber composition.
Thus, it is desired that such coloration for a portion of the tread be located primarily in the tread grooves and is primarily exclusive of the outer surface of a tread lug designed to be ground contacting.
In the description of this invention, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d if used herein, may be used interchangeably, unless otherwise prescribed. The terms xe2x80x9crubber compositionxe2x80x9d, xe2x80x9ccompounded rubberxe2x80x9d and xe2x80x9crubber compoundxe2x80x9d, if used herein, are used interchangeably to refer to xe2x80x9crubber which has been blended or mixed with various ingredients and materialsxe2x80x9d and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
In the description of this invention, the term xe2x80x9cphrxe2x80x9d refers to parts of a respective material per 100 parts by weight of rubber, or elastomer. The terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d may be used interchangeably unless otherwise indicate. The terms xe2x80x9ccurexe2x80x9d and xe2x80x9cvulcanizexe2x80x9d may be used interchangeably unless otherwise indicated.
In accordance with this invention, a pneumatic tire is provided having a multi-colored tread of a cap/base construction and a lug and groove construction wherein a visible portion of said grooves have walls of a non-black colored, devoid of carbon black, silica reinforced, rubber composition wherein and a majority of the visible portion of the surface of said tread is of a black-colored, carbon black-containing, rubber composition wherein said tread is comprised of co-extruded laminae of
(A) a layer of a carbon black-containing, black colored tread cap rubber composition configured with lugs and grooves wherein the outer surface, or face, said tread lugs are designed to be ground-contacting,
(B) a layer of a carbon black-containing, black-colored tread base which underlies said tread cap and is not designed to be ground contacting,
(C) a pair of carbon black-containing, black-colored tread miniwings extending from the peripheral edges of said tread, and
(D) at least one thin overlaying layer of said non-black colored, silica reinforced, outer rubber layer, exclusive of carbon black and containing a colorant other than of a black color, overlaying at least a portion of the surface of said at least a portion of said tread grooves.
In one aspect of the invention, said thin overlay rubber strip
(1) is positioned exclusively on at least a portion of the surface of at least a portion of said tread grooves and wherein a majority of the visible surface of the tread surface is of a black colored, carbon black containing, rubber composition, or
(2) is abraded away from the face of said lugs intended to be ground-contacting, or
(3) extends between the peripheral edge of said tread and said tread wings, or
(4) is positioned as a plurality of said co-extruded overlaying, non-black colored rubber strips are positioned over at least a portion of a plurality of the surface of said tread grooves exclusive of the face of said grooves intended to be ground-contacting.
In the practice of this invention, said thin, non-black colored co-extruded overlay rubber layer is comprised of
(A) 100 phr of elastomer comprised of
(1) about 20 to about 100, alternately about 50 to about 90, phr of at least one diene-based elastomer and
(2) from zero to about 80, alternately about 10 to about 50, phr of a halogenated copolymer of isobutylene and p-methyl styrene, wherein said halogen is selected from bromine or chlorine, preferably bromine,
(B) about 25 to about 100, alternately about 35 to about 90, phr of silica comprised of particulate synthetic amorphous silica selected from at least one of
(1) aggregates of precipitated silica having hydroxyl groups (e.g. silanol groups) on the surface thereof, and
(2) pre-hydrophobated aggregates of precipitated silica having been pre-hydrophobated by treating silica in an aqueous colloidal form thereof with both an organomercaptosilane and an alkylsilane in a weight ratio of said organomercaptosilane to said alkylsilane in a range of from 10/90 to 90/10;
wherein said alkylsilane is of the general Formula (I)
Xnxe2x80x94Sixe2x80x94R4-nxe2x80x83xe2x80x83(I) 
wherein R is an alkyl radical having from one to 18, preferably from one to 8, carbon atoms such as, for example, methyl, ethyl, isopropyl, n-butyl and octadecyl radicals, n is a value of from 1 to 3 and X is a radical selected from halogen, namely chlorine or bromine, preferably a chlorine radical, and alkoxy radicals, preferably an alkoxy radical as (OR1)xe2x80x94, wherein R1 is an alkyl radical having from one to 3 carbon atoms such as, for example, methyl, ethyl and isopropyl radicals, preferably from methyl and ethyl radicals, and where said organomercaptosilane is of the general formula (II):
(X)n(R2O)3-nxe2x80x94Sixe2x80x94R3xe2x80x94SHxe2x80x83xe2x80x83(II) 
wherein X is a radical selected from halogen, namely chlorine or bromine, preferably a chlorine radical, and alkyl radicals having from one to 16, preferably from one to 4, carbon atoms, preferably selected from methyl, ethyl, n-propyl and n-butyl radicals; wherein R2 is an alkyl radical having from one to 16, preferably from one to 4 carbon atoms, preferably selected from methyl and ethyl radicals and R3 is an alkylene radical having from one to 16, preferably from one to 4, carbon atoms, preferably a propylene radical; n is a value from zero to 3, preferably zero;
(3) about 0 to about 15, alternately about 1 to about 10, phr of a coupling agent having a moiety reactive with hydroxyl groups contained on the surface of said aggregates of precipitated silica and another moiety interactive with said diene-based elastomer(s);
(4) about 0.5 to about 20, alternatively about 2 to about 15, phr of an organo phosphite where said elastomer includes said halogenated copolymer, as at least one of organo diphosphites selected from diisodecyl pentearythritol diphosphite, distearyl pentaerythritol diphosphite and pentearythritol diphosphite and organo monophosphites selected from the general formulas (III) and (IV): 
((OR4)2xe2x80x94Pxe2x80x94Oxe2x80x94R5)2xe2x80x94R6xe2x80x83xe2x80x83(IV) 
wherein each R4 radical is independently selected from alkyl radicals and phenyl radicals and alkyl substituted phenyl radicals; wherein said R4 alkyl radicals have from 1 to 18 carbon atoms, preferably from 1 through 4 or from 4 through 12, carbon atoms, and preferably selected from methyl, ethyl, propyl radicals, from propyl, butyl, octyl and ethylhexyl radicals or from phenyl radicals; wherein said alkyl radicals for said alkyl substituted phenyl radicals have from 3 to 9 carbon atoms, wherein R5 is a phenyl radical; and wherein R6 is selected from alkyl radicals having from 2 to 8 carbon atoms preferably selected from ethyl, propyl and butyl radicals;
wherein said organo phosphite is preferably selected from the organo phosphites of said formula (I);
wherein said organo phosphite is provided by one or more of the following:
(a) by mixing said organo phosphite with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer,
(b) by pre-reacting said halogenated copolymer of isobutylene and p-methyl styrene with said organo phosphite prior to blending said reinforcing filler therewith,
(c) by pre-reacting said organo phosphite with an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form an organo phosphite/silica composite thereof,
(d) mixing said organo phosphite with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, according to any of said steps (a), (b) or (c) wherein said synthetic silica includes at least one of said pre-hydrophobated silica aggregates which has been pre-hydrophobated prior to mixing with said elastomers,
(e) mixing said organo phosphite with said elastomer(s) and an alkylsilane of the said Formula (I) with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, and
(f) by pre-reacting said organo phosphite and said alkylsilane of Formula (I) with
(i) said aggregates of synthetic precipitated silica or
(ii) an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form a silica composite thereof.
In the practice of this invention, said coupling agent for said aggregates of precipitated silica may preferably be, for example, an alkoxysilyl polysulfide such as for example, a bis(3-trialkoxysilylalkyl) polysulfide wherein alkyl radicals for said alkoxy groups are selected from one or more of methyl and ethyl radicals, preferably an ethyl radical and the alkyl radical for said silylalkyl component is selected from butyl, propyl and amyl radicals, preferably a propyl radical and wherein said polysulfide component contains from 2 to 8, with an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge.
Representative of such other coupling agents are, for example, bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge.
Such coupling agent may, for example, be added directly to the elastomer mixture or may be added as a composite of precipitated silica and such coupling agent formed by treating a precipitated silica therewith or by treating a colloidal silica therewith and precipitating the resulting composite.
In one aspect of the invention, said non-black colored rubber composition is preferably devoid of rubber processing oil other than paraffinic rubber processing oil which contains less than 14 weight percent aromatic compounds and is preferably devoid of antidegradants other than phenolic antidegradants, and also preferably contains said brominated poly(isobutylene-co-para-methylstyrene) compound.
In practice, a purpose of said coupling agent is to aid in enabling said amorphous silica to reinforce the rubber composition. For example, such coupling agent may be a coupling agent having a moiety reactive with hydroxyl groups contained on the surface of the amorphous silica (e.g. silanol groups) and another moiety interactive with at least one of said diene-based elastomers. Alternatively, said coupling agent may be contained on the silica itself wherein the silica has been pretreated with a coupling agent prior to its addition to the rubber composition.
Representative of such brominated poly(isobutylene-co-para-methylstyrene) copolymers is Exxpro 3745 from the ExxonMobil Chemical Company. In practice, a purpose of said coupling agent is to aid in enabling said amorphous silica to reinforce the rubber composition, although in a case where said pre-hydrophobated silica inherently contains a coupling agent, use of an additional coupling agent is not believed to be necessary. For example, such coupling agent may be a coupling agent having a moiety reactive with hydroxyl groups contained on the surface of the amorphous silica (e.g. silanol groups) and another moiety interactive with at least one of said diene-based elastomers. Alternatively, said coupling agent may be contained on the silica itself wherein the silica has been pretreated with a coupling agent prior to its addition to the rubber composition.
In practice, the pre-hydrophobated precipitated silica aggregates might be recovered, for example, from said treated colloidal silica, for example as a treated silica hydrosol, with the aid of acid addition to the treated colloidal silica (for example, sulfuric acid or hydrochloric acid) followed by water washing and drying the recovered hydrophobated silica as a hydrophobated silica gel or as a hydrophobated precipitated silica. While this invention is not intended to be directed to a specific preparation technique (preparation of silica hydrosols, recovery of silica gels and precipitated silicas, etc.) of the pre-hydrophobated precipitated silica itself, for education purposes in this regard, reference might be made to the Encyclopedia of Chemical Technology, Fourth Edition (1997), Volume 21, Kirk-Othmer in Pages 1020 through 1026 and U.S. Pat. No. 5,094,829 as well as U.S. Pat. Nos. 5,708,069, 5,789,514 and 5,750,610 for a more detailed discussion.
Representative alkylsilanes of Formula (I) are, for example, trichloro methyl silane, dichloro dimethyl silane, chloro trimethyl silane, trimethoxy methyl silane, dimethoxy dimethyl silane, methoxy trimethyl silane, trimethoxy propyl silane, trimethoxy octyl silane, trimethoxy hexadecyl silane, dimethoxy dipropyl silane, triethoxy methyl silane, triethoxy propyl silane, triethoxy octyl silane, and diethoxy dimethyl silane.
Representative examples of organomercaptosilanes of Formula (II), namely organomercaptosilanes are, for example, triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, and tripropoxy mercaptopropyl silane.
Representative examples of organo phosphites understood to be commercially available are, for example, triisodecyl phosphite, trilauryl phosphite, tris(tridecyl) phosphite, diphenyl isooctyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, triphenyl phosphite, triisononylphenyl phosphite, trimethyl phosphite, triethyl phosphite, tris (2-chloroethyl) phosphite, triisopropyl phosphite, tributyl phosphite, triisooctyl phosphite and tris (2-ethylhexyl) phosphite, as well as tris (2,4-di-t-butylphenyl) phosphite, and bis 2,4,6,tri-t-butylphenyl 2-butyl-2-ethyl-1,3-propanediol phosphite; and diphosphites as, for example, distearyl pentaerythritol diphosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, bis (2,6,di,t-butyl-4-methylphenyl pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol diphosphite and mixtures thereof.
Such organo phosphite may be, for example, tris (2-ethylhexyl) phosphite or triphenyl phosphite.
It is preferred that an in situ reaction of said organo phosphite and silica, optionally including the alkylsilane of formula (I), within the elastomer host may be accomplished without an evolution of an alcohol as compared to using the aforesaid alkoxysilyl polysulfide coupling agent by the inherent chemistry of the organo phosphite material and hydroxyl groups contained on the surface of said silica material in which water evolved instead of an alcohol as a byproduct of the reaction.
In the further practice of the invention, the aforesaid in situ reaction of said organo phosphite silica material within the elastomer host via said internal rubber mixing process is accomplished wherein said silica material is a precipitated silica and/or silica-containing carbon black which is hydrophobated prior to its addition to the elastomer (pre-hydrophobated). Such in situ reaction is considered herein to be important as to both the process of mixing and reacting of the organo phosphite and pre-hydrophobated silica material as to a resulting product thereof. In particular, is it considered herein that pre-hydrophobation of the silica material, particularly with an alkyl silane of the general formula (I) enables a more efficient mixing, or processing, of it within the elastomer host in that such pre-hydrophobation of the silica material
(A) renders it more compatible with the diene-based elastomer and
(B) substantially reduces a tendency for a precipitated silica to agglomerate with itself within the elastomer host.
In the practice of this invention, said pre-hydrophobated precipitated silica aggregates may be pre-hydrophobated, for example, by treating silica in an aqueous colloidal form thereof with said alkylsilane of Formula (I).
In another aspect of the invention, said elastomer composition for said non-black colored tread rubber layer(s) and for rubber composition(s) in direct contact with said non-black colored tread rubber layer(s) of is preferably devoid of rubber processing oil other than paraffinic rubber processing oils which contains less than 8 weight percent aromatic compounds and is preferably devoid of antidegradants other than phenolic antidegradants and is thus devoid of amine based antidegradants.